The S54 was never based on the M54. The S54 was improved from the S52, which was the engine used by the E36 M3 in Europe. The S52/S54 engine were bespoke M engines with no relation to the M series engines used on series cars from what i know.

All M3 engine until now which were based on AG engines only share the basic engine block layout with their AG counterparts ... really all other parts were bespoken part only developed for the S50s and the S54 (the special US M engines are an other story!).

BUT if BMW today speaks in the case of the F8x about an "heavily" modified N55 as basis and you also know that only cost reduction were the reason to choose this engine alternative ... it seem clear that "this engine" must be the cheapest possible way to reach the needed ~450hp ... so "heavily modified" meens in my opinion:- stronger engine block/crankcase by puting struts on the outside
- better/greater Turbos-system by using the TriTurbo of the N57S
- adding the newest VANOS availiable
- intelligent software
... plus some minor parts ... I think that would be all and I donīt define this as "heavily modified", its only an AG N55 with some better (newer) parts. If the M-GmbH would modify the N55 more heavily the cost would rise sharply and thats against all whats the BMW AG sought to achieve the BMW AG with its engine decision.

It will be a great car for sure and better than the C AMG, but that inline 6 is the only reason why I picked up mine off the lot this year.
I also hope that exhaust sounds much better than it does in that video...
The first and the last M3 with a V8 is gone...

I really hope this is not the final exhaust note ...... It sounds like my flatulent grandfather after a hearty bowl of chilli. Lets hope they slapped on straight pipes for these test runs and the retail version will have more of a low end growl rather than these baffs and lets hope the top end of the engine is smooth yet grunty without being obnoxious unless you really mash the pedal and give her the beans, THEN lets hear that engine go buck wild. Perhaps placing it in M mode should control the actual exhaust note via a valve of sorts and not turn on super secret sounds in the cabin ... Yeah I know I want the world blah blah blah

idk but i might be mistaking here so dont go crazy on me, but the new f80 M3 seems like the front and rear fender flares do not stick/poke out wider like they used to on the old M3s. Maybe its the camo and i cant tell but the body looks like a regular f30 with the same size fenders and rear quarter panel???? Thats just my observation. i could b wrong. Thanx 4 the help family!!!

idk but i might be mistaking here so dont go crazy on me, but the new f80 M3 seems like the front and rear fender flares do not stick/poke out wider like they used to on the old M3s. Maybe its the camo and i cant tell but the body looks like a regular f30 with the same size fenders and rear quarter panel???? Thats just my observation. i could b wrong. Thanx 4 the help family!!!

Take a look at all the spy photos of the F80 M3. The fenders flare dramatically.